1. Field of the Invention
This invention relates to resins and, more particularly, to ambient, temperature-stable mixtures of epoxy-labile hydrogen monomers and a latent catalyst.
2. Description of the Prior Art
Currently available epoxy-resin formulations are marketed as two component systems, the resin and curing agent. The packaging and utilization of these two-part epoxides present the disadvantages of package bulkiness and resin property variations due to improper proportioning and mixing. Substantial effort has been and is now being directed towards new packaging, metering and mixing techniques designed to alleviate these problems. Premixed, one-component systems containing the resin and cure catalyst circumvent these difficulties. However, in most cases the pot life of the catalyzed resin is impractically short; that is, on the order of minutes at room temperature.
Recently it has been discovered that polymers can be produced by the reaction of imides, acids or anhydrides with polyepoxides in the presence of chromium II salts having unoccupied coordination sites. The reaction appears to proceed rapidly at temperatures from 100.degree.C to 150.degree.C (as opposed to about 300.degree.C for other approaches), and does not produce water or any other by-products. At the present time, most polyimide compositions are sold as polyamic acid solutions. Solvent must be removed prior to use and volatiles are removed during cure.
Since no by-products are evolved, these polymers are amenable to standard bag molding techniques for preparing fiber reinforced structures, thus reducing fabrication costs and rendering the polymers useful in the fabrication of large structures. The polyimides are also useful as adhesives since the absence of by-products eliminates the need for high pressures for bonding and are also useful as heat-set potting compounds for encapsulation of electrical components. The polyesters will also find use as films for wire wrapping, motor insulation, surface coatings, lacquers, textile fibers, molding resins, fiberglass laminates for use in aircraft parts, honeycombs, forms as well as intermediates for producing other chemical compounds.
The chromium III salt catalysts provide rapid cure of these epoxy systems even at ambient temperature. However, the pot life is extremely limited and requires separate packaging and metering and mixing very near in time to fabrication.